Aluminum metallic nanoparticle-polymer nanocomposites for energy storage

ABSTRACT

A nanoparticle composition comprising a substrate comprising aluminum nanoparticles, an Al 2 O 3  component coating said aluminum nanoparticles, and a metallocene catalyst component coupled to the Al 2 O 3  component; and a polyolefin component coupled to said substrate.

This application is a continuation-in-part of and claims prioritybenefit from co-pending application Ser. No. 13/449,750 filed Apr. 18,2012, a divisional application of application Ser. No. 11/985,930 filedNov. 19, 2007, now issued as U.S. Pat. No. 8,163,347, which claimspriority benefit from application Ser. No. 60/859,873 filed on Nov. 17,2006, the entirety of which is incorporated herein by reference.

This invention was made with government support under N00014-05-1-0766awarded by the Office of Naval Research; DE-FG02-86ER13511 awarded bythe Department of Energy; and DMR1121262 awarded by the National ScienceFoundation. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Future pulsed-power and power electronic capacitors will requiredielectric materials ultimately having energy storage densities >30J/cm³, with operating voltages >10 kV, and msec/μsec charge/dischargetimes with reliable operation near the dielectric breakdown limit.Importantly, at 2 J/cm³ and 0.2 J/cm³, respectively, the operatingcharacteristics of current state-of-the-art pulsed power and powerelectronic capacitors, which utilize either ceramics or polymers asdielectric materials, remain significantly short of this goal. An orderof magnitude improvement in energy density will require development ofrevolutionary new materials that substantially increase intrinsicdielectric energy densities while operating reliably near the dielectricbreakdown limit. For simple linear response dielectric materials, energydensity is defined in eq. 1, where ∈_(r) is relative dielectricpermittivity, E is the dielectric breakdown strength, and ∈₀ is thevacuum permittivity. Generally, inorganic metal oxides exhibit highpermittivities, however, they suffer from low breakdown fields. Whileorganic materials (e.g., polymers) can provide high breakdown strengths,their generally low permittivities have limited their application.

U _(e)=½∈_(r)∈₀ E ²  (1)

Recently, inorganic-polymer nanocomposite materials have attracted greatinterest due to their potential for high energy density. By integratingthe complementary properties of their constituents, such materials cansimultaneously derive high permittivity from the inorganic inclusionsand high breakdown strength, mechanical flexibility, facileprocessability, light weight, and properties tunability (molecularweight, comonomer incorporation, thermal properties, etc.) from thepolymer host matrix. Additionally, there are good reasons to believethat the large inclusion-matrix interfacial areas will afford higherpolarization levels, dielectric response, and breakdown strength.

Although inorganic-polymer nanocomposites can be prepared via mechanicalblending, solution mixing, in situ radical polymerization, and in situnanoparticle synthesis, host-guest incompatibilities frequently resultin nanoparticle aggregation and phase separation, detrimental to theelectrical properties. Covalently grafting polymer chains to inorganicnanoparticle surfaces has also proven promising, leading to moreeffective dispersion and enhanced properties, however, such processesmay not be cost-effective and nor easily scaled up.

Illustrating another approach, in the large-scale heterogeneous orslurry olefin polymerizations practiced on a huge industrial scale, SiO₂is generally used as the catalyst support. However, very large localhydraulic pressures arising from the growing polyolefin chains are knownto effect extensive SiO₂ particle fracture and lead to SiO₂-polyolefincomposites. As a result, there remains an on-going search in the art foran alternate route to inorganic-polymer nanocomposites, to betterutilize the benefits and advantages afforded by such materials.

SUMMARY OF THE INVENTION

In light of the foregoing, it is an object of the present invention toprovide various high energy nanocomposites, related components anddevices, and/or methods for their preparation and/or assembly, therebyovercoming various deficiencies and shortcomings of the prior art,including those outlined above. It will be understood by those skilledin the art that one or more aspects of this invention can meet certainobjectives, while one or more other aspects can meet certain otherobjectives. Each objective may not apply equally, in all of itsrespects, to every aspect of this invention. As such, the followingobjects can be viewed in the alternative with respect to any one aspectof this invention.

It can be an object of the present invention to provide one or moremethods for nanocomposite preparation to prevent nanoparticleagglomeration problems associated with the prior art.

It can be another object of the present invention to provide an in situpolymerization technique using one or more metallocene catalystcomponents supported on a nanoparticle, with a range of available olefinmonomers.

It can be another object of the present invention, alone or inconjunction with one of the preceding objectives, to provide ananocomposite comprising a nanoparticle component homogeneouslydispersed within a matrix of a high-strength, high-energy commoditypolymer material of the sort used in the art with energy storagecapacitors and insulators.

Other objects, features, benefits and advantages of the presentinvention will be apparent from this summary and the followingdescriptions of certain embodiments, and will be readily apparent tothose skilled in the art having knowledge of various high energynanocomposites and assembly/production techniques. Such objects,features, benefits and advantages will be apparent from the above astaken into conjunction with the accompanying examples, data, figures andall reasonable inferences to be drawn therefrom, alone or withconsideration of the references incorporated herein.

In part, the present application can be directed to a particulatecomposition comprising a substrate comprising a metal oxide componentand an aluminum oxide component; and a metallocene olefin polymerizationcatalyst component coupled to such a substrate. Without limitation, sucha substrate and/or particulate can be nano-dimensioned. In certain otherembodiments, such a substrate and/or particulate composition can bemicro-dimensioned.

In certain embodiments, a metal oxide can be but is not limited tobinary and ternary metal oxides, such oxides as can comprise a dopant,and combinations thereof. In certain such embodiments, a metal oxidecomponent can be selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, BaTiO₃ BaZrO₃,PbO₃, together with Pb(TiZr)O₃ and other such oxides comprising adopant. Regardless, a metallocene component can be selected from anysuch polymerization catalyst known to those skilled in the art, madeaware of this invention. Without limitation, such a metallocenecomponent can be selected from EBIZrCl₂, CGCTiCl₂ and CpTiCl₃, asdescribed more fully below, and structural variations thereof. Withoutlimitation as to metal oxide and metallocene identity, such acomposition can be provided in a polyolefin matrix.

In part, the present invention can also be directed to a compositecomprising a nano-dimensioned substrate comprising a metal oxidecomponent, an aluminum oxide component and a metallocene catalystcomponent; and a polyolefin component coupled thereto. In certainembodiments, a polyolfin component can be selected from C₂ to about C₁₂polyalkylenes, substituted C₂ to about C₁₂ polyalkylenes, and copolymersthereof, such polyolefin components limited only by alkylene monomer (s)reactive with such a metallocene catalyst component under polymerizationconditions of the sort described herein. In certain such embodiments,metallocene and metal oxide components can be as described above orillustrated elsewhere herein. Accordingly, with choice of alkylenemonomer(s), such a polyolefin component can be select from isotacticpolypropylene, a linear polyethylene, and a polystyrene and copolymersthereof.

In part, the present invention can also be directed to a commodity orbulk material composition comprising a polyolefin component and anano-dimensioned or micro-dimensioned substrate component dispersedtherein, with such a substrate component comprising a metal oxidecomponent, an aluminum oxide component and metallocene catalystcomponent. Such metal oxide, aluminum oxide and metallocene componentscan be as described above. Without limitation as to substrate identity,volume fractions or percentages can range from about 0.05 percent toabout 15 percent. Likewise, substrate dispersion can be substantiallyhomogeneous on a nano- or microscale dimension. In certain suchembodiments, a metal oxide component of such a substrate can have ashape about or substantially spherical or a shape about or substantiallyrod-like, as demonstrated below.

A polyolefin component of such a composition is limited only by monomerpolymerization in the presence in such a metallocene catalyst. Forinstance, in certain embodiments, a polyolefin can be selected from C₂to about C₁₂ polyalkylenes, substituted C₂ to about C₁₂ polyalkylenes,and copolymers thereof. Regardless, depending upon polyolefin and/orsubstrate component identity, such a composition can be present as athin film and/or incorporated into a range of device structures,including but not limited to insulator devices. Alternatively, dependingupon a particular composition, such materials can find utility in thecontext of cable insulation.

In part, the present invention can also be directed to a method ofpreparing a metal oxide-polyolefin nanocomposite. Such a method cancomprise providing a substrate comprising a metal oxide component and ametallocene olefin polymerization catalyst component coupled thereto;and contacting such a substrate with an olefin component, such contactfor a time and/or an amount sufficient to at least partially polymerizean olefin on such a substrate, to provide a nanocomposite. Withoutlimitation, metal oxide, metallocene and/or olefin/alkylene componentscan be selected as described above. Depending upon olefin content anddegree of polymerization, such a substrate component can have a volumepercentage ranging from about 0.05 percent to about 15 percent. Incertain, embodiments, increasing volume percent can be used to affectmelt temperature, leak current density and/or relative permittivity of aresulting nanocomposite. In certain other embodiments, choice of metaloxide shape can be used to affect one or more composite physicalcharacteristics. Without limitation, the relative permittivity of such ananocomposite can be increased using a rod-shaped metal oxide component.

Illustrating yet another aspect thereof, the present invention can bedirected to a method of using an aluminoxane component to moderate phaseenergy densities of a metal oxide-polyolefin composite. Such a methodcan comprise providing a metal oxide component as can be selected frombinary and ternary metal oxides and such oxides comprising a dopant;contacting such a metal oxide component with an aluminoxane componentfor a time at least partially sufficient to provide an aluminum oxidecoating on the metal oxide component; contacting such a coated metaloxide with a metallocene olefin polymerization catalyst component, toprovide a nano- or micro-dimensioned substrate of the sort describedabove; and contacting such substrate with one or more olefin components,such contact for a time and/or an amount sufficient to at leastpartially polymerize the olefin(s) on such a substrate.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1. ¹³C NMR spectrum of an isotactic-polypropylene nanocomposite(100 MHz, C₂D₂Cl₄, 130° C.).

FIG. 2. ¹³C NMR spectrum of a poly(ethylene-co-1-octene) nanocomposite(100 MHz, C₂D₂Cl₄, 130° C.).

FIG. 3. ¹³C NMR spectrum of a syndiotactic-polystyrene nanocomposite(100 MHz, C₂D₂Cl₄, 130° C.).

FIGS. 4A-B. Electron microscopic characterization of: (A) as-receivedpristine ZrO₂ (SEM) and (B) 7.4 vol % ZrO₂-^(iso)PP nanocomposite (TEM).

FIGS. 5A-B. Electron microscopic characterization of: (A) as-receivedpristine TZ3Y (SEM) and (B) 31.1 wt % TZ3Y-^(iso)PP nanocomposite (TEM).

FIGS. 6A-B. Electron microscopic characterization of: (A) as-receivedpristine TZ8Y (SEM) and (B) 39.2 wt % TZ8Y-^(iso)PP nanocomposite (TEM).

FIG. 7. Representative C (capacitance) vs. A (electrode area) plot for a2.6 vol % BaTiO₃-^(iso)PP nanocomposite.

FIGS. 8A-C. Leakage current density vs. field measurement results forthe nanocomposite MIS or MIM devices (legends are for the volumefraction of the inorganic particles): (A) n⁺—Si/BaTiO₃-polypropylene/Au;(B) n⁺—Si/sphere-TiO₂-polypropylene/Au; (C)Al/rod-TiO₂-polypropylene/Au.

FIGS. 9A-C. Leakage current density vs. field measurement results forthe nanocomposite MIS or MIM devices (legends are for the volumefraction of the inorganic particles): (A)Al/ZrO₂-polypropylene/Au; (B)Al/TZ3Y-polypropylene/Au; (C) Al/TZ8Y-polypropylene/Au.

FIG. 10. Normalized effective permittivity (∈_(eff)-∈_(b)/∈_(a)∈_(b))for composite dielectrics of polypropylene with spherical inclusions(eq. 6), and with ellipsoidal inclusions (eq. 7).

FIG. 11. Comparison of effective permittivities for spherical- androd-shaped TiO₂ nanoparticle-polypropylene nanocomposites.

FIG. 12. Real (∈′) and imaginary (∈″) parts of the complex permittivityfor a material having interfacial, orientational, ionic, and electronicpolarization.

FIG. 13. Depiction of possible orientations of an aligned two-particleaggregate compared to a single isolate particle when an applied voltageinduces charges on each of the electrodes; the correspondingpolarization of the particles within the matrix results in chargeaccumulation at the particle surface, wherein the response of thesecharges to the oscillating field is the Maxwell-Wagner-Sillars (MWS)polarization.

FIG. 14. (A) Photograph of a thick film prepared in a PET washer, andTEM of (B) Al nanoparticles after washing, (C) as fabricated compositepowder and (D) melt-processed composite powder of the 0.104 v_(f)composite where the dark spots are nanoparticles; as well as, SEMcharacterization of a 0.104 v_(f) composite (E) thick film surface and(F) thin film torn edge.

FIG. 15. Permittivity of Al-^(iso) nanocomposites from 100 MHz to 7 GHzas a function of Al nanoparticle volume fraction.

FIG. 16. Graph showing tan δ of Al-^(iso) nanocomposites as a functionof nanoparticle volume fraction from 100 MHz-7 GHz.

FIG. 17. Representation of Al nanoparticle-polypropylene compositesynthesis.

FIG. 18. Examples of metallocene polymerization catalysts.

FIG. 19. Scheme 1. Synthesis of Isotactic Polypropylene-Metal OxideNanocomposites.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Illustrating certain embodiments of this invention, high energy densityBaTiO₃- and TiO₂-isotactic polypropylene nanocomposites were preparedvia in situ metallocene polymerization. The resulting nanocompositeswere found to have effective nanoparticle dispersion and to possessenergy densities as high as 9.4 J/cm³, as determined from relativepermittivities and dielectric breakdown measurements. To demonstratevarious other aspects of this invention, the scope of inorganicinclusion can be extended to include a broad variety of nanoparticles,with corresponding effects of nanoparticle identity and shape on theelectrical/dielectric properties of the resulting nanocomposites.Likewise, the scope of metallocene polymerization catalysts and olefinicmonomers can be extended (e.g., Chart 1, FIG. 18) to enhancenanoparticle processability and thermal stability. Representative of arange such of embodiments, nanoparticle coating with methylaluminoxane(MAO) and subsequent in situ polymerization can be used effectively foreffective dispersion, to realize high breakdown strengths,permittivities and energy storage densities.

Accordingly, a series of 0-3 metal oxide-polyolefin nanocomposites wassynthesized via in situ olefin polymerization using the metallocenecatalysts C₂-symmetric dichloro[rac-ethylenebisindenyl]zirconium(IV)(EBIZrCl₂), Me₂Si(^(t)BuN)(η⁵-C₅Me₄)TiCl₂ (CGCTiCl₂), and(η⁵-C₅Me₅)TiCl₃ (Cp*TiCl₃) immobilized on methylaluminoxane(MAO)-treated barium titanate (BaTiO₃), zirconium dioxide (ZrO₂), 3 mol% yttria-stabilized zirconia (TZ3Y), 8 mol % yttria-stabilized zirconia(TZ8Y), sphere-shaped titanium dioxide (TiO₂), and rod-shaped TiO₂nanoparticles. The resulting composite materials were characterized byX-ray diffraction (XRD), scanning electron microscopy (SEM),transmission electron microscopy (TEM), ¹³C nuclear magnetic resonance(NMR) spectroscopy, and differential scanning calorimetry (DSC). It wasshown by TEM that the nanoparticles are well-dispersed in the polymermatrix and each individual nanoparticle is surrounded by polymer.Electrical measurements reveal that most of the nanocomposites haveleakage current densities 10⁻⁸-10⁻⁶ A/cm², and the relativepermittivities of the nanocomposites increase as the nanoparticle volumefraction increases, with measured values as high as 6.1. At the samevolume fraction, rod-shaped TiO₂ nanoparticle-polypropylenenanocomposites exhibit greater relative permittivities than thecorresponding sphere-shaped TiO₂ nanoparticle-polypropylenenanocomposites. The energy densities of these nanocomposites areestimated to be as high as 9.4 J/cm³.

In another embodiment, metal nanoparticle-polyolefin composites wereprepared by chemisorbing a metallocene precatalyst, for example[rac-ethylenebisindenyl]zirconium dichloride (EBIZrCl₂), onto a nativeoxide of Al nanoparticles. Addition of a methylaluminoxane (MAO)co-catalyst then activated the adsorbed EBIZrCl₂ for in situ synthesisof isotatic polypropylene. Capacitors were then fabricated with films ofthese materials for dielectric characterization. As seen in otherceramic composites fabricated using the in situ polymerization method,the present composite films have no discernible voids and thetransmission electron microscopy (TEM) and scanning electron microscopy(SEM) images of the films indicate uniform morphologies (FIG. 14). Thenative Al₂O₃ coating on the particles is ˜2 nm thick as confirmed byTEM. It is noted that this oxide thickness is comparable to that of asingle Al₂O₃ layer derived from exposing methylaluminoxide (MAO) to air,and is thin enough that the volume fraction of Al metal in the samplesis equivalent to the volume fraction of nanofiller.

In yet another embodiment, and depending upon polyolefin and/orsubstrate component identity, a composition according to the inventioncan be present as a thin film. Thin film capacitors as produced by theinstant invention can be used in diverse high frequency electronicapplications ranging from signal coupling, filtering, and impedancematching to advanced packaging applications.

As one of the most commonly used polymers in large-scale powercapacitors, isotactic polypropylene offers greater stiffness, lowershrinkage, and less deterioration of the dielectric properties at highertemperatures than other grade polypropylenes. Therefore, theC₂-symmetric metallocene catalystdichloro[rac-ethylenebisindenyl]zirconium(IV) (EBIZrCl₂), known forhighly isospecific olefin polymerization, was selected to demonstrateimmobilization on the surfaces of MAO-treated metal oxide nanoparticles,to synthesize metal oxide-isotactic polypropylene nanocomposites. X-raydiffraction (XRD) linewidth analyses using the Scherrer equationindicate that the microstructures and coherence lengths of theindividual nanoparticles remain largely unchanged upon deagglomerization(Table 1). (See, Jenkins, R.; Snyder, R. L. InIntroduction to X-rayPowder Diffractometry; Winefordner, J. D., Ed.; Wiley: New York, 1996;pp 89-91; and Scherrer, P. Gött. Nachr. 1918, 2, 98-100.) ¹³C NMRspectroscopy (FIG. 1) shows that the present polypropylenes are highlyisotactic, as evidenced by the isotacticity index ([mmmm]=83%). (See,Busico, V.; Cipullo, R.; Monaco, G.; Vacatello, M. Macromolecules 1997,30, 6251-6263; Busico, V.; Cipullo, R.; Corradini, P.; Landriani, L.;Vacatello, M.; Segre, A. L. Macromolecules 1995, 28, 1887-1892; andZambelli, A.; Dorman, D. E.; Brewster, A. I. R.; Bovey, F. A.Macromolecules 1973, 6, 925-926.) DSC confirms the absence of extensiveamorphous regions in the composites since only isotactic polypropylenemelting features (142-147° C.) are detected. XRD data for thenanocomposites also reveal the presence of monoclinic a phasecrystalline isotactic polypropylene (2θ=14.2, 17.0, 18.6, and 21.8°). Itis found that the melting temperatures of the nanocomposites generallyincrease as the nanoparticle loading increases (Table 2), possibly dueto attractive interactions between the nanoparticles and the crystallineregions of the isotactic polypropylene.

TABLE 1 XRD Linewidth Analysis Results of the Nanocomposites 2θ FWHMCrystallite Powder (deg) (deg) Size (nm) BaTiO₃-polypropylene 31.6490.271 32.8 BaTiO₃ 31.412 0.254 35.6 TiO₂-polypropylene 25.358 0.361 23.5TiO₂ 25.360 0.317 27.1 Crystallite size (L) is calculated using theScherrer equation L = 0.9λ/Bcosθ_(B) (λ = x-ray wavelength, B =full-width-at-half maximum (FWHM) of the diffraction peak, and θ_(B) =Bragg angle).

Linear low-density polyethylene (LLDPE) is another polymer that iswidely used in power capacitors. Compared to isotactic polypropylene,the chain branching in the LLDPE affords better processability.Therefore, the sterically open constrained geometry catalystMe₂Si(^(t)BuN)(η⁵-C₅Me₄)TiCl₂ (CGCTiCl₂) was utilized to synthesizeBaTiO₃-LLDPE nanocomposites via in situ ethylene+1-octenecopolymerization. FIG. 2 presents a representative ¹³C NMR spectrum ofthe nanocomposite, with the 1-octene incorporation level calculated tobe 25.0 mol %. (See, Qiu, X.; Redwine, D.; Gobbi, G.; Nuamthanom, A.;Rinaldi, P. L. Macromolecules 2007, 40, ASAP.) DSC measurements alsoconfirms the formation of LLDPE, which has a typical melting temperatureof 125.3° C.

Syndiotactic polystyrene has greater heat resistance than isotacticpolypropylene, which can only operate below 85° C. when incorporatedinto film capacitors. Employing the same protocol as EBIZrCl₂, thehalf-metallocene catalyst Cp*TiCl₃ ²⁵ was immobilized on MAO-treatedZrO₂ nanoparticles. Subsequent in situ styrene polymerization affordsZrO₂-syndiotactic polystyrene nanocomposites. A representative ¹³C NMRspectrum is shown in FIG. 3. The characteristic single resonance nearδ=145.6 ppm for the ipso phenyl carbon atom confirms the production ofsyndiotactic polystyrene, which is further substantiated by the meltingtemperature (267.0° C.) as measured by DSC.

During the course of in situ metallocene polymerization, the polymerchains propagating at the nanoparticle-immobilized metallocene catalyticcenters may be expected to create large local hydrostatic pressures andthus help to disrupt the nanoparticle agglomeration. Such results areconfirmed by the comparative electron microscopic characterization ofthe as-received pristine nanoparticles and the resulting nanocomposites.As can be seen from FIGS. 4, 5, and 6, the as-received pristinenanoparticles evidence very high levels of agglomeration, however, forthe polyolefin nanocomposites, the agglomeration of the nanoparticles isshown to be disrupted and each individual nanoparticle is surrounded bya layer of matrix polymer.

To assess nanocomposite permittivity properties, metal-insulator-metal(MIM) or metal-insulator-semiconductor (MIS) devices for nanocompositeelectrical measurements were fabricated by first doctor-bladingnanocomposite films onto aluminum or n⁺-Si substrates, followed byvacuum-depositing top gold electrodes through shadow masks. Thecapacitances were measured at 1 kHz, a sufficiently high frequency toavoid the complications arising from conduction and interfacialpolarization effects. After the capacitance was measured at multiplelocations on the nanocomposite film surface using different electrodeareas, the relative permittivity (∈_(r)) of the nanocomposite wasderived using eq. 2, where C is the capacitance, A is the electrodearea,

$\begin{matrix}{C = \frac{ɛ_{0}ɛ_{r}A}{d}} & (2)\end{matrix}$

∈₀ is the vacuum permittivity (8.8542×10⁻¹² F/m), ∈_(r) is relativepermittivity, and d is the nanocomposite film thickness. FIG. 7 shows arepresentative capacitance vs. electrode area plot, the linearity ofwhich indicates the good dielectric uniformity of the nanocompositefilm.

Table 2 summarizes the relative permittivity measurement results for thepresent nanocomposites. As the nanoparticle loading increases, therelative permittivity of the nanocomposites also increases as predictedby the effective medium approximation. At the same volume fraction,rod-shaped TiO₂-polypropylene nanocomposites exhibit significantlygreater relative permittivities than those prepared with sphere-shapedTiO₂ nanoparticles (compare entries 1-4 versus 11-13) under identicalreaction conditions. Without limitation, this shape effect is thought toarise from the different depolarization factors for different inclusionparticle geometries.

TABLE 2 Electrical Characterization Results for MetalOxide-polypropylene Nanocomposites^(a) Film Nanoparticle T_(m) ^(c)Breakdown Thickness^(e) Energy Density^(f) Entry Composite vol %^(b) (°C.) Permittivity^(d) Field (kV) (μm) (J/cm³) 1 ^(iso)PP-^(s)TiO₂ 0.1%135.2 2.2 ± 0.1 >10.0 36 >0.8 ± 0.1  2 ^(iso)PP-^(s)TiO₂ 1.6% 142.4 2.8± 0.2 9.5 23 2.1 ± 0.2 3 ^(iso)PP-^(s)TiO₂ 3.1% 142.6 2.8 ± 0.1 7.5 271.0 ± 0.1 4 ^(iso)PP-^(s)TiO₂ 6.2% 144.8 3.0 ± 0.2 9.3 20 2.8 ± 0.2 5^(iso)PP-BaTiO₃ 0.5% 136.8 2.7 ± 0.1 8.8 28 1.2 ± 0.1 6 ^(iso)PP-BaTiO₃0.9% 142.8 3.1 ± 1.2 >10.0 21 >4.0 ± 0.6  7 ^(iso)PP-BaTiO₃ 2.6% 142.12.7 ± 0.2 9.8 25 1.8 ± 0.2 8 ^(iso)PP-BaTiO₃ 5.2% 145.6 2.9 ± 1.0 8.2 301.0 ± 0.3 9 ^(iso)PP-BaTiO₃ 6.7% 144.8 5.1 ± 1.7 9.0 22 3.7 ± 1.2 10^(iso)PP-BaTiO₃ 13.6% 144.8 6.1 ± 0.9 >10.0 17 >9.4 ± 1.3  11^(iso)PP-^(r)TiO₂ 1.4% 139.7 3.4 ± 0.3 12 ^(iso)PP-^(r)TiO₂ 3.2% 142.44.1 ± 0.7 13 ^(iso)PP-^(r)TiO₂ 5.1% 143.7 4.9 ± 0.4 14 ^(iso)PP-ZrO₂1.6% 142.9 1.7 ± 0.3 15 ^(iso)PP-ZrO₂ 3.9% 145.2 2.0 ± 0.4 16^(iso)PP-ZrO₂ 7.5% 144.9 4.8 ± 1.1 17 ^(iso)PP-ZrO₂ 9.4% 144.4 5.1 ± 1.318 ^(iso)PP-TZ3Y 1.1% 142.9 1.1 ± 0.1 19 ^(iso)PP-TZ3Y 3.1% 143.5 1.8 ±0.2 20 ^(iso)PP-TZ3Y 4.3% 143.8 2.0 ± 0.2 21 ^(iso)PP-TZ3Y 6.7% 144.92.7 ± 0.2 22 ^(iso)PP-TZ8Y 0.9% 142.9 1.4 ± 0.1 23 ^(iso)PP-TZ8Y 2.9%143.2 1.8 ± 0.1 24 ^(iso)PP-TZ8Y 3.8% 143.2 2.0 ± 0.2 25 ^(iso)PP-TZ8Y6.6% 146.2 2.4 ± 0.4 ^(a)Polymerizations carried out in 50 mL of tolueneunder 1.0 atm of propylene at 20° C. ^(b)From elemental analysis.^(c)From differential scanning calorimetry. ^(d)Derived from capacitancemeasurement. ^(e)Film thicknesses measured using profilometry.^(f)Energy density (U) calculated from U = 0.5ε₀ε_(r)E_(b) ² (ε₀, vacuumpermittivity; ε_(r), relative permittivity; and E_(b), breakdown field(MV/cm) calculated by dividing breakdown voltage by film thickness).

The leakage current densities of all the nanocomposite films prepared inthis investigation (FIGS. 8 and 9) are mostly within the range 10⁻⁸-10⁻⁶A/cm² at 100 V, indicating that the aforementioned nanocomposites areall excellent insulators. As the nanoparticle loading increases, most ofthe nanocomposites exhibit lower leakage current densities, presumably aresult of modified charge transport and interruption of the crystallineconduction pathways within the composite structure. However, at thehighest nanoparticle loadings, the nanocomposites have the largestleakage current densities, simply because the weight percentages of thenanoparticles have reached the respective percolation thresholds.Increasing the relative permittivity of the nanocomposite by changingthe shape of the inclusion does not appear to compromise the goodinsulating properties of these composites.

The present measured breakdown strengths for some of the nanocompositesare invariably ˜3-6 MV/cm, indicating that metal oxide nanoparticleinclusion does not significantly depress the polymer dielectricbreakdown strength. Without limitation, in a well-dispersed nanoparticlecomposite, interfaces between the ceramic nanoparticles and polymerphases can create effective electron scatterers and trapping centers,thus reducing the breakdown probability. Moreover, well-dispersedceramic nanoparticles may block degradation tree growth and can increasethe long-term breakdown strength. Energy densities of the presentnanocomposites are estimated to be as high as 9.4 J/cm³, which rivals orexceeds those reported for conventional ceramic, polymer, and compositedielectrics.

A challenge in the preparation of inorganic metal oxide-polyolefinnanocomposites is the general phase incompatibility between inorganicpolar metal oxide inclusions and the non-polar organic host materials.For example, ferroelectric metal oxides are highly hydrophilic, whileisotactic polypropylene is highly hydrophobic. Simple admixing of thetwo constituents negligibly disrupts the extensive nanoparticleagglomeration nor affects the um-scale or larger phase separation, whichcan lead to local dielectric breakdown and degrade the nanocompositeelectrical properties. In contrast, the present in situ supportedmetallocene polymerization approach minimizes these deficiencies byachieving homogeneous nanoscale dispersion of the metal oxide phase:each individual nanoparticle is surrounded by polymer chains propagatingin situ from the surface-immobilized metallocenium catalyst centers, andthus offers improved dielectric properties (energy densities as high as9.4 J/cm³).

However, such nanocomposites can have very large contrasts in relativepermittivities between host and guest materials, leading to a largedisparity in the electric fields within the constituent phases, thuspreventing the realization of maximum energy densities for bothconstituents simultaneously. For representative BaTiO₃-polypropylenenanocomposites, however, the achieved energy density is as high as 9.4J/cm³ although the materials permittivity ratio approaches ˜1000:1.Without limitation to any one theory or mode of operation, the Al₂O₃(∈_(r)≈10) layer (thickness 1 nm, estimated from ICP-OES analysis)evolving from ambient exposure of the MAO coating, can act as adielectric buffer layer between the high permittivity BaTiO₃nanoparticles (∈_(r)≈2000) and low permittivity polypropylene (E_(r) z2.2).

As discussed above, the aforementioned in situ synthetic approach wasalso applied to metallic nanoparticles having a native metal oxidecoating. As a non-limiting example thereof, metallic aluminumnanoparticles are coated with a metal oxide coating, such as, forexample, Al₂O₃, wherein the oxide coating is, for example, 2 nm thick(see FIG. 17). It was found that the complex permittivity of themetallic Al particles affords composites with high permittivities, up to˜15 at 100 Hz, and significant recoverable energy storage of up to ˜14J/cm³. These composites maintain permittivities greater than 10 up to 1MHz, with only the highest Al volume fraction (0.12) material exhibitingsignificant relaxation in the 100 Hz to 1 MHz range. While Al isspecifically mentioned, it will be understood that other metalnanoparticles other than aluminum can be employed to produce similarresults.

With regard to characterizing the aluminum nanoparticle materialsprepared according to the invention, the frequency dependence ofpermittivities is conventionally measured using dielectric relaxationspectroscopy (DRS) which probes the interaction of the sample with atime-dependent electric field. The resulting polarization, expressed bythe frequency-dependent complex permittivity (here by the realpermittivity and tan δ), characterizes the amplitude and timescale ofcharge density fluctuations across the sample. Such fluctuationsgenerally arise from electronic polarization, or more significantly, thereorientation of permanent molecular dipole moments, of nanoparticles orof dipolar moieties appended to polymers. Other possible mechanismsinclude ion transport or the reorganization of interfacial charge inheterogeneous systems, with the timescale of the fluctuations dependingon the material and the relevant relaxation mechanism. Relaxationtimescales range from psec in low-viscosity liquids to hours in glasses,with the corresponding frequencies encompassing 0.1 mHz-1 THz, (FIG.12). In FIG. 12, the frequencies shown are typical of homogenousmaterials reported in the literature, with the type of relaxation andapproximate characteristic frequency indicated.

Since in all polarization mechanisms (except those at opticalfrequencies arising from electronic polarization) the dipolar responseto an oscillating field involves displacement of masses, inertiaconstrains arbitrarily rapid movements. Two physical parameters describethe movement of the charged masses in response to alternating fields,polarization response and relaxation. Response can be modeledkinematically and relaxation describes the decay of polarization fromexcited states to the ground state. For every response mechanismoperative in a material, the polarization decays below certain limitingfrequencies above which the dipole can no longer reorient with the speedof the fluctuating field. As noted above, each response type has acharacteristic relaxation frequency as shown in FIG. 12. Whilerelaxation frequencies are typically in the GHz region, electronicpolarization responds to very high frequencies (optical, ˜1000 THz) andlimits the index of refraction (n≈√{square root over (ε_(r))}). Incontrast, interfacial polarization often decays at low frequencies(sometimes <1 MHz) and ionic polarization has resonances between GHz andoptical frequencies. Maxwell-Wagner-Sillars polarization is theinterfacial polarization between the internal dielectric boundary layersin a material, and generally occurs between the (slower) macroscopicinterfacial relaxation at the electrode-dielectric layer interface andthe (faster) orientational relaxation in the GHz range. While bothMaxwell-Wagner-Sillars (MWS) polarization and macroscopic interfacialpolarization are due to the reorganization of charges at surfaces, MWSpolarization contributes orders of magnitude less to the permittivitythan does the electrode interface polarization due to the microscopicnature of the internal dielectric surfaces. However, MWS also exhibitspolarization response until much higher frequencies because there arefar fewer charges that must reorganize in the oscillating field,resulting in lower reorganization energies and potential fasterreorganization times.

As described herein, the frequency response of the aforementionedAl-polypropylene nanocomposites are analyzed between 200 MHz and 7 GHzto understand the types of dielectric relaxation operative in thepresent metallic nanocomposites. From Maxwell-Wagner-Sillars modeling,it is appears that conductive particle aggregation leads to strongdielectric relaxation, where increasing aggregate size depresses therelaxation frequencies. Mixing approaches such as percolation theory,which accurately predict permittivities for typical nanocomposites atlow frequencies, argue that higher volume fractions of extremely highpermittivity nanoparticles (∈_(r)>2000) lead to aggregates (e.g.,chains) of particles that behave like single particles (at least fortransport). For ferroelectric materials, such particle chains arethought to exhibit a combined dipole moment which responds to the field,resulting in dipolar polarization. In contrast, conductive particlesurfaces instead accumulate charge at interfaces with the matrix, whicheffectively thin the dielectric layer and cause additional interfacialMWS polarization (FIG. 13). These internal interfacial polarizations canbe a major component of the dielectric response of the material and arehighly sensitive to the orientation and alignment of the chargeaccumulation surfaces. MWS modeling offers a means to quantify the lossand frequency dependence of this polarization. Using geometricalarguments based on the conductive particle shape and orientation, MWStheory predicts that at high metallic nanoparticle volume fractions,above the percolation threshold (v_(f)=0.16), particle aggregation willsignificantly lower the relaxation frequency. Accordingly, it is shownthat above ˜0.10 volume fraction and to about 0.125 volume fraction,Al-polypropylene nanocomposites have relatively high permittivities thatare sustainable up to at least 5 GHz, and that composites with high Alvolume fractions undergo relaxation at lower frequencies than theirlower volume fraction counterparts.

The complex reflection (both magnitude, Γ, and phase, θ) for aluminumnanocomposite capacitors was measured using lumped impedance methods.From the magnitude and phase of the complex reflection, the dielectricpermittivities (eq. 3) of the thick films can be calculated. Here ω isthe radial frequency, C_(o)=A_(∈o)/d, wherein A is the area, d is thethickness of the sample, and Z_(o) the characteristic impedance of alossless transmission line (50Ω).

$\begin{matrix}{ɛ_{r}^{''} = \frac{2\; \Gamma \; \sin \; \theta}{\omega \; C_{o}{Z_{o}\left( {\Gamma^{2} + {2\; \Gamma \; \cos \; \theta} + 1} \right)}}} & (3)\end{matrix}$

FIG. 15 summarizes the frequency-dependent permittivity of Al-^(iso)PPnanocomposites as a function of composition from 200 MHz to 7 GHz. Forthe lowest volume fraction Al nanocomposites (0.007-0.029), the highfrequency permittivities are statistically indistinguishable and ˜2.This is consistent both with the low measured permittivities at lowerfrequencies and the fact that these samples have very little MWSpolarization but instead are expected to have dielectric relaxationdominated by optical relaxations which occur at frequencies higher than7 GHz. The 0.104 volume fraction composite has a permittivity ˜10 at 1MHz but experiences a relaxation between 1 and 200 MHz, and thedielectric permittivity falls to ˜6 by 200 MHz, and falls further as 7GHz is approached. The permittivity of the 0.124 composite begins toundergo a dielectric relaxation before 1 M decreases by ˜50% between 1and 200 MHz and appears to have another relaxation near 5 GHz.Nevertheless, it maintains a permittivity >5 at frequencies between 200MHz and 5 GHz. The observed relaxations in the hundreds of MHz are mostlikely a result of MWS interfacial relaxations while the relaxations inthe GHz range may also be orientational polarization relaxations fromthe polymer matrix. In polymer films, typical orientational relaxationsarise from dipolar groups attached to the backbone and smalloscillations of the chain geometries, especially reorientation of chainends.

It is seen that while the 0.104 and 0.124 volume fraction Alnanocomposites undergo a dielectric relaxation and permittivity decreaseof almost 50% between 1 and 200 MHz, they maintain relatively largepermittivities (˜6) in the 1 MHz-7 Ghz range, and preferably in the 200MHz-7 GHz range. It is also noted that these materials appear to undergoanother relaxation around 5-7 GHz. Relatively frequency-insensitive,high permittivities in the GHz range make these composites idealcandidates for high frequency dielectric applications. The ceramicparticle counterparts to these composites all have permittivities below2 by 100 MHz and common radio frequency dielectrics have permittivitieson the order of 3-4.

The value of tan δ is the imaginary part divided by the real part of thepermittivity (tan δ=∈″/∈′).

$\begin{matrix}{ɛ_{r}^{''} = \frac{1 - \Gamma^{2}}{\omega \; C_{o}{Z_{o}\left( {\Gamma^{2} + {2\; \Gamma \; \cos \; \theta} + 1} \right)}}} & (4)\end{matrix}$

By calculating both the real part (eq 3) and the imaginary part (eq 4)of the permittivity from the measured complex reflection, tan δ isobtained (FIG. 16). Because the present lumped impedance techniquemeasures the permittivity via a reflection method, there is some noisein the derived imaginary part of the permittivity, which introduces tanδ noise due to the very high measured magnitude of the reflection, Γ.The loss, tan δ, is proportional to the difference between thereflection magnitude of the sample and perfect reflection (100%). Lumpedimpedance measurements are typically limited to higher loss systems,however, since the measured tan δ here is greater than 0.02, this is nota major concern. However, overall these composites have relatively lowloss, since up to 7 GHz the loss remains below 0.20.

As expected from the trends in permittivity, the tan δ of the 0.124volume fraction Al nanocomposite begins to rise dramatically around 1GHz, resulting in the permittivity fall evident in FIG. 15. For both the0.104 and 0.124 volume fraction materials, the permittivity data suggesta dielectric relaxation in the MHz range, but since the accuracy of thetan δ data in this region does not allow extraction of the exactfrequency of this relaxation, the maximum in tan δ is notwell-determined. Such GHz frequency relaxations seen in the high volumefraction polymer composites are most often attributed to orientationalrelaxation such as rotation of dipolar groups around bonds, chaintwisting or libration. In ordered polymers lacking dipolar groups as inisotatic polypropylene, such polarizations have been assigned to chainend rotation, and therefore this relaxation is a fairly small fractionof the total response. Because the polypropylene is grown in situ on thenanoparticle surfaces, the higher volume fraction nanocomposites shouldhave greater surface areas, hence higher chain end densities, and hencegreater contributions from reorientational polarization processes,likely enhancing the relaxation processes observed at >3 GHz.Nevertheless, the 0.10 of Al-^(iso)PP nanocomposite is the most usefulmaterial for GHz range capacitor applications since the permittivity of˜6 is maintained above 5 GHz.

The most common effective medium models for permittivity are derived forthe simple case of a spherical dielectric inclusion embedded in a sphereof the host material. However, most materials do not occur naturally asspheres, and therefore effective medium models for other shapes havealso been developed. (See, e.g., Brosseau, C.; Beroual, A.; Boudida, A.J. Appl. Phys. 2000, 88, 7278-7288; Green, N. G.; Jones, T. B. J. Phys.D: Appl. Phys. 2007, 40, 78-85.) Simple analytical solutions for theeffective permittivity (∈_(eff)) can be derived only for ellipsoids,whereas all other shapes require numerical solutions. Depolarizationfactors along each semi-axis of the ellipsoid (N_(x), N_(y), N_(z)),where N_(x)=N_(y)=N_(z)=1, can be used to estimate geometrical effects.The depolarization factors are calculated from integrals, e.g., eq. 5,where a_(x), a_(y), a_(z) are the semi-axes of the ellipsoid. Forspheres, all three

$\begin{matrix}{N_{x} = {\frac{a_{x}a_{y}a_{z}}{2}{\int_{0}^{\infty}{\frac{1}{\left( {s + a_{x}^{2}} \right)\sqrt{\left( {s + a_{x}^{2}} \right)\left( {s + a_{y}^{2}} \right)\left( {s + a_{z}^{2}} \right)}}\ {s}}}}} & (5)\end{matrix}$

depolarization factors are equal (⅓, ⅓, ⅓), however, for ellipsoids thedepolarization factors are, 0, ½, ½, respectively and for discs, 1, 0,0, respectively. Since the dielectric energy is a stationary functionalof the electric field, the result is that permittivities arising fromspherical inclusions are the lowest and any deviation from the sphericalshape results in an increase in the effective permittivity of themixture at the same volume fraction. These observations prompted studyof TiO₂-isotactic polypropylene nanocomposites with different inclusionshapes.

In FIG. 10, the calculated effective permittivities of thenanocomposites containing spherical inclusions to the nanocomposites arecompared with ellipsoidal inclusions. For the case of sphericalinclusions, the effective permittivities are calculated using theMaxwell-Garnett effective medium theory (eq. 6), and for the case ofellipsoidal inclusions,

$\begin{matrix}{ɛ_{eff} = {ɛ_{b}\frac{ɛ_{a} + {2\; ɛ_{b}} + {2\; {f_{a}\left( {ɛ_{a} - ɛ_{b}} \right)}}}{ɛ_{a} + {2\; ɛ_{b}} - {2\; {f_{a}\left( {ɛ_{a} - ɛ_{b}} \right)}}}}} & (6) \\{ɛ_{eff} = {ɛ_{b} + {\frac{f_{a}}{3}\left( {ɛ_{a} - ɛ_{b}} \right){\sum\limits_{{j = x},y,z}^{\;}\; \frac{ɛ_{eff}}{ɛ_{eff} + {N_{j}\left( {ɛ_{a} - ɛ_{eff}} \right)}}}}}} & (7)\end{matrix}$

the effective permittivities are calculated using the Polder-Van Santenformalism (eq. 7), where ∈_(a) is the relative permittivity of the TiO₂inclusions, ∈_(b) is the relative permittivity of isotacticpolypropylene, f_(a) is the volume fraction of TiO₂ in the polymer, andN_(j) is for the depolarization factors. (See, e,g., Busico, V.;Cipullo, R.; Monaco, G.; Vacatello, M. Macromolecules 1997, 30,6251-6263.) As expected, the effective medium theory predicts thatcomposites containing ellipsoidal inclusions will have larger effectivepermittivities at low volume loadings than composites containingspherical inclusions.

The experimental results are plotted in FIG. 11. Remarkably, theeffective permittivities for spherical inclusions remain constant over asmall range of volume fractions, exactly as the Maxwell-Garnett equationpredicts (FIG. 10). In marked contrast, the effective permittivity ofcomposites having inclusions with ellipsoidal shapes increases rapidlywith increasing inclusion volume fraction, which is again similar totrend predicted for ellipsoidal inclusions using eq. 7 (FIG. 10).

Examples of the Invention

Materials and Methods. All manipulations of air-sensitive materials wereperformed with rigorous exclusion of oxygen and moisture in flamedSchlenk-type glassware on a dual-manifold Schlenk line or interfaced toa high-vacuum line (10⁻⁵ Torr), or in a dinitrogen-filled VacuumAtmospheres glove box with a high capacity recirculator (<1 ppm O₂ andH₂O). Propylene (Matheson, polymerization grade) was purified by passagethrough a supported MnO oxygen-removal column and an activated Davison 4Å molecular sieve column. Toluene was dried using an activated aluminacolumn and Q-5 columns according to the method described in literature,and was additionally vacuum-transferred from Na/K alloy and stored inTeflon-valve sealed bulbs for polymerization manipulations. BaTiO₃ andTiO₂ nanoparticles were kindly provided by Prof. Fatih Dogan (Universityof Missouri, Rolla) and Prof. Thomas Shrout (Penn State University),respectively. ZrO₂ nanoparticles were purchased from Aldrich. Thereagents 3 mol % yttria-stabilized zirconia (TZ3Y) and 8 mol %yttria-stabilized zirconia (TZ8Y) nanoparticles were purchased fromTosoh, Inc. TiO₂ nanorods were purchased from Reade Advanced Materials,Riverside, R.I. All of the nanoparticles were dried on a high vacuumline (10⁻⁵ Torr) at 80° C. overnight to remove the surface-bound water,known to adversely affect the dielectric breakdown performance. Thedeuterated solvent 1,1,2,2-tetrachloroethane-d₂ was purchased fromCambridge Isotope Laboratories (≧99 atom % D) and used as received.Methylaluminoxane (MAO; Aldrich) was purified by removing all thevolatiles in vacuo from a 1.0 M solution in toluene. The reagentdichloro[rac-ethylenebisindenyl]zirconium (IV) (EBIZrCl₂) was purchasedfrom Aldrich and used as received. n⁺—Si wafers (rms roughness≈0.5 nm)were obtained from Montco Silicon Tech (Spring City, Pa.) and cleanedaccording to standard procedures. Aluminum substrates were purchasedfrom McMaster-Carr (Chicago, Ill.) and cleaned according to standardprocedures.

Physical and Analytical Measurements. NMR spectra were recorded on aVarian Innova 400 (FT 400 MHz, ¹H; 100 MHz, ¹³C) spectrometer. Chemicalshifts (δ) for ¹³C spectra were referenced using internal solventresonances and are reported relative to tetramethylsilane. ¹³C NMRassays of polymer microstructure were conducted in1,1,2,2-tetrachloroethane-d₂ containing 0.05 M Cr(acac)₃ at 130° C.Resonances were assigned according to the literature for stereoregularpolypropylenes. Elemental analyses were performed by Midwest Microlabs,LLC, Indianapolis, Ind. Inductively coupled plasma-optical emissionspectroscopy (ICP-OES) analyses were performed by GalbraithLaboratories, Inc., Knoxyille, Tenn. The thickness of the dielectricfilm was measured with a Tencor P-10 step profilometer and used tocalculate the dielectric constant and breakdown strength of the sample.X-ray powder diffraction patterns were recorded on a Rigaku DMAX-Adiffractometer with Ni-filtered Cu Kα radiation (1.54184 Å). Pristineceramic nanoparticles and composite microstructures were examined with aFEI Quanta sFEG environmental scanning electron microscope with anaccelerating voltage of 30 kV. Transmission electron microscopy wasperformed on a Hitachi H-8100 TEM with an accelerating voltage of 200kV. Composite melting temperatures were measured on a TA Instruments2920 temperature modulated differential scanning calorimeter. Typically,ca. 10 mg samples were examined, and a ramp rate of 10° C./min was usedto measure the melting point. To erase thermal history effects, allsamples were subjected to two melt-freeze cycles. The data from thesecond melt-freeze cycle are presented here.

Electrical Measurements.

Gold electrodes for metal-insulator-semiconductor (MIS) devices werevacuum-deposited through shadow masks at (3-4) δ 10⁻⁶ Torr (500 Å,0.2-0.5 Å/s). Direct current MIS leakage current measurements wereperformed using Keithley 6430 sub-femtoamp remote source meter and aKeithley 2400 source meter using a locally written LABVIEW program andgeneral purpose interface bus communication. A digital capacitance meter(Model 3000, GLK Instruments, San Diego) was used for capacitancemeasurements. All measurements were performed under ambient conditions.Dielectric breakdown strength measurements were carried out with ahigh-voltage amplifier (TREK 30/20A, TREK, Inc., Medina, New York), andthe experimental parameters were: ramp rate, 1,000 V/S; peak voltage,30,000 V; ext. amplifier, 3,000; temperature, room temperature.

With reference to the following representative examples, any metal oxidecomponent, metallocene catalyst component, aluminoxane component andolefin monomer component of the sort described herein can be usedinterchangeably with any one of the other. Accordingly, the generalprocedures of examples 1-2 were used to prepare the range ofnanocomposites referenced in conjunction with the corresponding figures,such procedures as can be modified by those skilled in the art madeaware of this invention. As such, the embodiments of example 3 were alsoprepared using such procedures (corresponding figures and data notshown).

Example 1 Representative immobilization of Metallocene Catalysts onMetal Oxide Nanoparticles

In the glovebox, 2.0 g nanoparticles, 200 mg MAO, and 50 mL dry toluenewere loaded into a predried 100 mL Schlenk flask. Upon stirring, themixture turned into a very fine slurry. The slurry was next subjected toalternating sonication and vigorous stirring for 2 days with constantremoval of evolving CH₄. Next, the nanoparticles were collected byfiltration and washed with fresh toluene (50 mL×4) to remove anyresidual MAO. Then, 200 mg metallocene catalyst was loaded in the flaskwith 50 mL toluene. The color of the nanoparticles immediately turnedpurple. The slurry mixture was again subjected to alternating sonicationand vigorous stirring overnight. The nanoparticles were then collectedby filtration and washed with fresh toluene until the color of thetoluene remained colorless. The nanoparticles were dried on thehigh-vacuum line overnight and stored in the glovebox at −40° C.

Example 2 Representative Synthesis of Nanocomposites via In SituPropylene Polymerization

In the glovebox, a 250 mL round-bottom three-neck Morton flask, whichhad been dried at 160° C. overnight and equipped with a large magneticstirring bar, was charged with 50 mL dry toluene, 200 mg functionalizednanoparticles, and 50 mg MAO. The assembled flask was removed from theglovebox and the contents were subjected to sonication for 30 min withvigorous stirring. The flask was then attached to a high vacuum line(10⁻⁵ Torr), freeze-pump-thaw degassed, equilibrated at the desiredreaction temperature using an external bath, and saturated with 1.0 atm(pressure control using a mercury bubbler) of rigorously purifiedpropylene while vigorously stirring. After a measured time interval, thepolymerization was quenched by the addition of 5 mL methanol, and thereaction mixture was then poured into 800 mL of methanol. The compositewas allowed to fully precipitate overnight and was then collected byfiltration, washed with fresh methanol, and dried on the high vacuumline overnight to constant weight.

Example 3

More specifically, with reference to the preceeding, BaTiO₃ and TiO₂ 40nm nanoparticles were dried on a high-vacuum line to removesurface-bound water, known to adversely affect dielectric breakdownperformance. Nanocomposites were then synthesized via sequentialnanoparticle MAO functionalization, catalyst immobilization/activation,and in situ isotactic propylene polymerization (Schemes 1 and 2, FIG.19). The first step is the anchoring MAO onto the nanoparticle surfacesvia surface hydroxyl group reaction to form covalent Al—O bonds.Anchored MAO functions as a cocatalyst to activate the metallocene, andin addition, the hydrophobic MAO helps disrupt, in combination withultrasonication, hydrophilic nanoparticle agglomeration in thehydrophobic reaction medium. After washing away unbound MAO, theMAO-coated nanoparticles are subjected to reaction with the C₂-symmetricpolymerization catalyst EBIZrCl₂ to afford surface-anchored,polymerization-active species. EBIZrCl₂ is known to produce highlyisotactic polypropylene, which, in conventional capacitors, affordsenhanced mechanical and dielectric properties at elevated operatingtemperatures. Subsequent in situ polymerization yields isotacticpolypropylene-BaTiO₃/TiO₂ nanocomposites, the compositions of which canbe tuned by the polymerization conditions.

Example 4

Al (d=100 nm) nanoparticles with 2 nm native Al₂O₃ were purchased fromSigma-Aldrich. From the TEM it is clear that the particles range fromabout 50 nm to 150 nm in diameter. The nanoparticles were dried on ahigh vacuum line (10⁻⁵ Torr) at 80° C. overnight to remove thesurface-bound water. The reagent [rac-ethylenebisindenyl]zirconiumdichloride was purchased from Sigma-Aldrich and used as received. MAO,10% solution in toluene, was also purchased from Sigma-Aldrich andpurified by removing the volatiles in vacuo. All manipulations ofair-sensitive materials were performed with rigorous exclusion of O₂ andmoisture using Schlenk techniques, or a high-vacuum line (10⁻⁶ Torr), ora N₂-filled MBraun glove box with a high capacity recirculator (<1 ppmO₂ and H₂O). Propylene (Matheson, polymerization grade) was purified bypassage through a supported MnO O₂-removal column and an activatedDavison 4 A molecular sieve column. Toluene was dried using an activatedalumina column and Q-5 columns, and is then vacuum-transferred from Na/Kalloy and stored in Teflon-valve sealed bulbs.

In the glovebox, 2.0 g of nanoparticles, 200 mg of the metalloceneprecatalyst EBIZrCl₂ and 50 mL of toluene were loaded into a predried200 mL flip-fit flask. The color of the particle suspension turned tolight orange. The slurry mixture was subjected to alternating sonicationand vigorous stirring overnight. The particles were then collected byfiltration and washed with fresh toluene until the color of the tolueneremained colorless. The particles were dried on the high-vacuum lineovernight and stored in the glovebox at −40° C. in the dark.

In the glovebox, a 250 mL round-bottom three-neck Morton flask, equippedwith a large magnetic stirring bar, was charged with 50 mL of drytoluene, 200 mg of the above catalyst-functionalized nanoparticles, and50 mg of MAO. The assembled flask was removed from the glovebox and themixture was subjected to sonication and vigorous stirring for 30 min.The flask was then attached to a high vacuum line (10⁻⁵ Torr), thecatalyst slurry was degassed, equilibrated at the desired reactiontemperature using an external water bath, and saturated with 1.0 atm(pressure control using a mercury bubbler) of rigorously purifiedpropylene while vigorously stirring. After a measured time interval(changing the interval results in different particle loadings), thepolymerization was quenched by the addition of 5 mL of methanol, and thereaction mixture was then poured into 800 mL of methanol. The compositewas allowed to fully precipitate overnight and was then collected byfiltration, washed with fresh methanol, and dried on the high vacuumline at 80° C. overnight to constant weight.

Elemental analyses were performed by Midwest Microlabs, LLC,Indianapolis, Ind. Inductively coupled plasma-optical emissionspectroscopy (ICP-OES) analyses were performed by GalbraithLaboratories, Inc., Knoxyille, Tenn.

Example 5

Films with diameters between 3 and 7 mm are required. To obtain filmsthat are robust to tearing at these diameters, relatively thick filmswere fabricated. The films were fabricated by slowly pressing thenanocomposite samples, that were heated slowly in a crucible until thecomposite powder was viscous (maximum surface temperature of crucibleand composite was 100° C.), into the openings of small metal or PETwashers, 3 mm in diameter and 1 mm thick. The thick films were thenpressed with additional composite powder using a hot press at 100° C.and 500-800 psi pressure. The pressing helps create the smoothestelectrode-dielectric interface possible. Postpressing vacuum treatmentat 80° C. was then performed overnight to remove any residual moistureand trapped air bubbles. Next, parallel-plate capacitors were fabricatedby vapor-depositing gold electrodes on the dielectric nanocompositefilms. Gold electrodes for metal insulator metal (MIM) devices werevacuum deposited through shadow masks at (3-4)×10⁻⁷ Torr (500 Å, 0.2-1.0Å/s). The films were then removed from the washers by either cuttingaway the PET washer or boring the sample out of the metal washer.

The thicknesses of the films were measured with calipers and used tocalculate the dielectric permittivity and tan δ. Film topography and RMSroughnesses were imaged using a JEOL SPM atomic force microscope. Thethick films had rms roughnesses of 3-4 nm. Low frequency (1 MHz)capacitance was measured on an HP 4384A precision meter.

High frequency capacitance was measured using a lumped impedance methodon an HP 8510 network analyzer whose sample holder terminated in an APC7connector. This connector was fitted with the “shorted coaxial cable”sample holder. Each 3 mm thick film sample was placed directly on thecenter of the APC7 and then enclosed in the sample holder. The sampleholder was fitted with an electrode at the end of a movable plungerwhich is brought into contact with the upper film surface by tighteningthe feed screw. In this configuration the sample holder inductance isminimized. To measure the high frequency capacitance, a lumped impedancemethod of measuring the complex reflection coefficient (both magnitude,Γ, and phase, θ) is utilized. By placing a thick sample (˜1 mm) at theend of the coaxial line, the reflection coefficient of the impedancetransported down the line can be measured. Before measuring an unknowncapacitor, a calibration was performed by attaching known standards(short, open, and load) to the end of the coaxial line.

As demonstrated, the present invention provides a range ofwell-dispersed metal oxide-polyolefin nanocomposites via a scalable, insitu supported metallocene olefin polymerization process. Leakagecurrent densities ˜10⁻⁸-10⁻⁶ A/cm² suggest that the nanocomposites areexcellent insulators. The relative permittivity of the nanocompositesincreases as the nanoparticle fraction increases. At the same inclusionloading, rod-shaped TiO₂ nanoparticle-polypropylene nanocompositesexhibit significantly greater relative permittivities than sphere-shapedTiO₂ nanoparticle-polypropylene nanocomposites. Energy densities of theBaTiO₃-polypropylene nanocomposites are found to be as high as 9.4J/cm³. Energy densities of the Al₂O₃-polypropylene nanocomposites arefound to be as high as about 14 J/cm³. This versatile approach offerseffective control over composite composition and ready scalability. Thatis, simply by varying nanoparticle identity as well as their sizes,shapes, and the metallocene catalysts used, a wide array ofnanocomposites with desired dielectric and mechanical properties canthus be catalytically synthesized in situ.

We claim:
 1. A solid nanoparticle composition comprising a substratecomprising a metal nanoparticle component and a metal oxide component;and a metallocene olefin polymerization catalyst component coupled tosaid metal oxide component of said substrate, wherein said metal oxidecomponent is homogenously dispersed throughout said nanocompositecomposition.
 2. The composition of claim 1 wherein said metallocenecomponent is EBIZrCl₂.
 3. The composition of claim 1 in a polyolefinmatrix.
 4. The composition of claim 3 wherein the polyolefin ispolypropylene.
 5. The composition of claim 4 wherein the metalnanoparticles are aluminum nanoparticles.
 6. The composition of claim 5wherein the metal oxide component is Al₂O₃.
 7. The composition of claim6 wherein the metal nanoparticles are coated by the metal oxidecomponent.
 8. A composite comprising a nano-dimensioned substratecomprising aluminum nanoparticles homogenously dispersed throughout saidsubstrate, an Al₂O₃ component coating said aluminum nanoparticles, and ametallocene catalyst component; and a polyolefin component coupled tosaid substrate.
 9. The composite of claim 8 wherein said polyolefincomponent is selected from C₂ to about C₁₂ polyalkylenes, substituted C₂to about C₁₂ polyalkylenes, and copolymers thereof.
 10. The composite ofclaim 8 wherein said metallocene component is EBIZrCl₂.
 11. Thecomposite of claim 10 wherein said polyolefin component is isotacticpolypropylene.
 12. The composite of claim 10 having an energy density ofabout 14 J/cm³.
 13. The composite of claim 10 wherein the Alnanoparticle volume fraction is from between 0.100 and 0.125.
 14. Thecomposite of claim 13 wherein the composite maintains a permittivity ofat least about 6 in the 1 MHz-7 GHz frequency range.
 15. The compositeof claim 8 wherein the Al nanoparticles are from 50-150 nm in diameter.16. A commodity material composition comprising a polyolefin componentand a nano-dimensioned substrate component dispersed therein, saidsubstrate component comprising a metal nanoparticle component, an Al₂O₃component, and a metallocene catalyst component.
 17. The composition ofclaim 16 wherein said substrate dispersion is substantially homogenouson a nanoscale dimension.
 18. The composition of claim 16 wherein saidpolyolefin component is selected from C₂ to about C₁₂ polyalkylenes,substituted C₂ to about C₁₂ polyalkylenes, and copolymers thereof. 19.The composition of claim 16 wherein the metal nanoparticle component isan aluminum nanoparticle component.
 20. The composition of claim 19 as athin film in an insulator device.